This invention relates in general to vehicle transmissions and in particular to an improved structure for supporting a bearing with a vehicle transmission case.
In most vehicles, a transmission is provided in the drive train between the engine and the driven wheels. As is well known, the transmission includes a case containing an input shaft, an output shaft, and a plurality of meshing gears which are selectively connected between the input shaft and the output shaft. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of speed reduction gear ratios between the input shaft and the output shaft. By appropriate selection of these meshing gears, a desired speed reduction gear ratio can be obtained between the input shaft and the output shaft. As a result, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.
Typically, this gear ratio selection is accomplished by moving one or more control members provided within the transmission case. Movement of the control member causes certain ones of the meshing gears to be connected between the input shaft and the output shaft so as to provide the desired gear ratio therebetween. In a manual transmission, movement of the control member is accomplished by manual exertion of the vehicle driver, such as through a shift lever. In an automatic transmission, movement of the control member is accomplished by a pneumatic or hydraulic actuator in response to predetermined operating conditions.
In many medium and heavy duty manual transmissions, the case of the transmission is divided into two or three portions. The forward portion of the transmission case is usually referred to as the clutch housing. The clutch housing is sized to extend over and protectively enclose a manually operable clutch connected between the engine of the vehicle and the input shaft of the transmission. The central portion of the transmission case is usually referred to as the main housing. The main housing contains most of the shafts, gears, and other components which are used to provide a group of gear ratios to operate the transmission. In compound transmissions (i.e., those transmissions which are composed of a first group of gear ratios provided by a main section and one or more additional groups of gear ratios provided by an auxiliary section), the transmission case may include a rear portion. The rear portion of the transmission case is usually referred to as the auxiliary housing and contains most of the shafts, gears, and other components which are used to provide the additional group or groups of gear ratios provided by the auxiliary section.
In a typical transmission, it is usually necessary to support the ends of one or more shafts for rotation. To accomplish this, it is well known to form some of the portions of the transmission case with cylindrical bores or recesses and to provide annular bearings within such bores for rotatably supporting the ends of the shafts. A typical annular bearing includes an inner race, an outer race, and a plurality of rollers, such as cylinders or balls, disposed between the races. The outer race is pressed into the cylindrical recess formed in the transmission case and is frictionally engaged therewith to prevent any relative rotational movement. Similarly, the inner race is frictionally engaged or otherwise secured to the shaft to prevent any rotational movement therebetween. Thus, the rollers accommodate all of the relative rotational movement between the outer race (connected to the transmission case) and the inner race (connected to the shaft). No relative rotational movement should occur between the outer race and the transmission case. Such movement can cause undesirable looseness which could lead to premature wear or failure.
In the past, the various housings of the transmission case have all been made from iron. Although iron is well suited for use in manufacturing each of these housings, it is also a relatively heavy material. Because of increasing concerns about fuel economy in vehicles, efforts have been made recently to reduce the weight of various vehicle components. As a result, it is known to use a lighter weight aluminum alloy to form the clutch housing of the transmission case, while continuing to form the main housing of the transmission case from iron.
In further developing the use of aluminum alloys to form the clutch housing of the transmission case, it has been discovered that the annular bearings used to rotatably support the ends of shafts on the aluminum clutch housing tended to lose their frictional engagement with the associated bores after operation of the transmission. It has been determined that this looseness is caused by a differential in the rates of thermal expansion between aluminum alloys and steel. The aluminum alloy used to form the clutch housing expands a relatively large amount as the temperature increases. The steel used to form the outer races of the annular bearings, on the other hand, expands a relatively small amount as the temperature increases. Consequently, the bores formed in the aluminum clutch housing expand radially to a significantly greater extent than the outer races of the annular bearings disposed therein. As a result, the side walls of the bores expand away from the outer races of the bearings when the temperature increases because of normal usage of the transmission. When this occurs, the outer races lose their frictional engagement with the associated bores. This looseness permits undesirable relative rotational movement between the outer race and the clutch housing. Conventional transmissions formed completely of iron do not experience this problem because the rates of thermal expansion of iron and steel are sufficiently similar as to prevent this from occurring. In aluminum housings, this problem can be addressed by use of a heavy interference fit between the bearing and the bore. Unfortunately, it causes installation problems since the soft aluminum bore is easily damaged when pressing the steel race with a high interference fit. This hinders installation and can cause bearing misalignment.
Thus, it would be desirable to provide an improved structure for supporting a bearing in a bore provided in a portion of a transmission case and for preventing relative rotation therebetween when the bearing and the transmission case are formed from materials having different rates of thermal expansion.